Abstract
Abstract. In January 2020, a scientific borehole planning workshop sponsored by the International Continental Scientific Drilling Program was convened at Cornell University in the northeastern United States. Cornell is planning to drill test wells to evaluate the potential to use geothermal heat from depths in the range of 2700–4500 m and rock temperatures of about 60 to 120 ∘C to heat its campus buildings. Cornell encourages the Earth sciences community to envision how these boreholes can also be used to advance high-priority subsurface research questions. Because nearly all scientific boreholes on the continents are targeted to examine iconic situations, there are large gaps in understanding of the “average” intraplate continental crust. Hence, there is uncommon and widely applicable value to boring and investigating a “boring” location. The workshop focused on designing projects to investigate the coupled thermal–chemical–hydrological–mechanical workings of continental crust. Connecting the practical and scientific goals of the boreholes are a set of currently unanswered questions that have a common root: the complex relationships among pore pressure, stress, and strain in a heterogeneous and discontinuous rock mass across conditions spanning from natural to human perturbations and short to long timescales. The need for data and subsurface characterization vital for decision-making around the prospective Cornell geothermal system provides opportunities for experimentation, measurement, and sampling that might lead to major advances in the understanding of hydrogeology, intraplate seismicity, and fluid/chemical cycling. Subsurface samples could also enable regional geological studies and geobiology research. Following the workshop, the U.S. Department of Energy awarded funds for a first exploratory borehole, whose proposed design and research plan rely extensively on the ICDP workshop recommendations.
Highlights
1 Introduction: a convergence of society’s need for low-carbon heat and Earth scientists’ need to understand continental crust
A strategy for a scientific borehole mission at Cornell University must be placed in the context of coexistence with a pair of boreholes planned to demonstrate the viability of producing geothermal fluid at a sufficient flow to meet 20 % of Cornell’s building heat needs
Given that the geothermal demonstration wells would be wide in diameter, cased through intervals that present environmental or borehole management risks, maintained in a disturbed condition if production is initiated, and necessarily that their operations would prioritize the success of the geothermal project, there would be both short-term design and long-term management challenges related to co-located scientific program activities
Summary
Central New York State in northeastern North America is just one location, yet its need for the conversion to a low-carbon energy source by which to warm residences and commercial buildings and to heat water is an extremely common situation for much of Earth’s population. The concept under evaluation by Cornell University, to utilize geothermal heat by tapping fluids in rock at temperatures in the range of 60–120 ◦C, could serve widely in New York State to heat residences and commercial buildings, for certain industrial activities, and to assist controlled agriculture operations for food production. New York State has banned high-volume hydraulic fracturing in horizontal wells, as practiced for production of gas or oil from organic-rich shale, the long-established use of hydraulic pressure to stimulate existing fractures remains legal Both the options of natural transmissivity and fluid flow through stimulated fractures are plausible fluid-flow pathways. Technical risks can be addressed by determining whether the sedimentary rock–basement interface is a relevant geothermal development target and under what rock conditions artificial stimulation could improve permeability to achieve adequate fluid flow and prolonged heat transfer to permit direct use of geothermal energy where continental crust is naturally of low permeability
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